Semifinished product made from a shape memory alloy having a two-way effect and method for manufacturing the same

ABSTRACT

The present invention relates to a semifinished product made from a shape memory alloy having a two-way effect, and to a method for manufacturing the same. An objective in this case is to produce a two-way effect in the shape memory alloy in simple fashion and using only few process steps, so that the semifinished product made of the shape memory alloy at the austenite/martensite phase transition, is able to pass through a large number of deformation cycles, and it exhibits high effect amounts, without requiring a protracted training of the shape memory alloy or externally acting forces. In one single deformation step, a linear, superelastic phase is additionally produced in the shape memory alloy, thereby introducing a restoring force to the shape memory alloy, so that, under the action of this restoring force, the shape memory alloy passes repeatedly through the deformation cycle during the austenite/martensite phase transition.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a semifinished product made froma shape memory alloy having a two-way effect, and to a method formanufacturing the same.

[0002] It is generally known that shape memory alloys (SMA) haveadvantageous properties in comparison to conventional structural-typematerials. Due to their ability to remember a specific shape in thelow-temperature martensite phase and in the high-temperature austenitephase, deformations can be achieved within a set temperature range overa large number of cycles.

[0003] When working with the austenite/martensite phase transition andits associated deformation, one can utilize two effects, namely theone-way effect and the two-way effect. In the case of the one-wayeffect, an element made of a shape-memory alloy, which had beenplastically deformed in the temperature range in which the alloy ispresent in the martensitic phase, begins to return to the shape beforedeformation when heated above the temperature at which thetransformation to the austenitic phase begins. The alloy remembers theoriginal shape and, in the austenitic phase, returns the element to itsundeformed state. However, when cooled to the martensitic state, theshape of the alloy does not change again. Thus, shape memory alloyshaving a one-way effect can only be used for a one-time reshaping.Shape-memory alloys of this kind are employed, for example, inconnection, fastening, and sealing technology, as well as for deploymentprocesses in aerospace.

[0004] The two-way effect describes the fact that the shape-memory alloyremembers both a specific shape in the high-temperature austenite phase,as well as one in the low-temperature martensite phase. This makes itpossible to pass several times through the deformation cycle. Thetransformation or reforming can be memorized because of an externalforce (extrinsic two-way effect) or because of repeated cycles ofstressing the alloy. The latter is also referred to as the intrinsictwo-way effect.

[0005] The intrinsic two-way effect requires a so-called training inorder to impress specific dislocation structures upon the alloy, whichcause the alloy, even when cooled, to revert to a desired or trainedshape. For this, the alloy is deformed in the martensitic state beyondthe martensite plateau, in order to also introduce plastic deformations,by way of dislocations, to the alloy. When heated, only a portion of thedeformation component reverts to the shape, because of the dislocations.When cooled, the plastic stress fields existing around the dislocationsproduce martensite variants, which transform the alloy into the desiredlow-temperature shape. For this purpose, the deformation is repeated intransformation cycles n-times, so that the internal stresses in theshape memory alloy stabilize, and the alloy memorizes the dislocationstructures. However, this means that, prior to its proper serviceapplication, the shape memory alloy must first be subjected to thistime-consuming training.

[0006] In the case of the extrinsic two-way effect, the action of anexternal force, such as a weight, a counterspring, or even an oppositeshape memory element, initially deforms the element in the martensiticstate. When heated to the austenitic state, a return to the shape beforedeformation (recovery) occurs at the martensite/austenite phasetransition. The subsequent cooling leads, under the action of theexternal force, to renewed deformation. Providing an external force tostimulate the two-way effect can be disadvantageous in manyapplications, since additional precautions must be taken to prepare andadjust the shape memory alloy and the external force.

[0007] U.S. Pat. No. 4,411,711 describes a method for producing areversible two-way shape memory effect in a component made from amaterial showing only a one-way shape memory effect. The component madeof a shape memory alloy, which, under normal conditions, exhibits only aone-way effect, is specially treated, so that a two-way effect isinduced in this component. For this, the shape memory alloy is firsttreated with a solution and is subsequently quenched in water. The shapememory alloy is then either shot peened using steel balls or workhardened.

SUMMARY OF THE INVENTION

[0008] Starting out from the related art, an object of the presentinvention is to produce a semifinished product from a shape memory alloyhaving a two-way effect. An additional or alternate object is to devisea method for fabricating such a semifinished product, the two-way effectbeing accomplished in the shape memory alloy in simple fashion and usingas few process steps as possible, so that, at the austenite/martensitephase transition, the semifinished product made of the shape memoryalloy is able to pass through a large number of deformation cycles andexhibits high effect amounts, without the need, beforehand, for aprotracted training of the shape memory alloy or for externally actingforces.

[0009] The present invention provides a semifinished product made from ashape memory alloy having a two-way effect, wherein, in addition to theactive martensitic/austenitic phase, the shape memory alloy includes alinear, superelastic phase, which results in a restoring force beingproduced in the shape memory alloy, so that, under the action of thisrestoring force, the shape memory alloy runs through the deformationcycle several times during the austenite/martensite phase transition.

[0010] Advantageously, the linear, superelastic phase is situated at theouter cross-sectional side of the semifinished product, and the activemartensitic/austenitic phase is situated in the mid-cross-sectional areaof the semifinished product. In response to heating, the martensiticphase may enter into the austenitic phase, under deformation of theshape memory alloy, and, in response to cooling, returns to themartensitic phase, the shape memory alloy returning to the shape beforedeformation, through the action of the restoring force.

[0011] The shape memory alloy may have stress distributions so thattensile and compressive forces are produced, which lead to a curvatureof the semifinished product. The tensile forces may run on the outercurvature side and the compressive forces on the inner curvature side ofthe semifinished product.

[0012] The shape memory alloy advantageously is an alloy which is ableto exhibit a two-way effect. The shape memory alloy may be composed of54.76 wt % nickel and of 45.23 wt % titanium.

[0013] The shape memory alloy, in the cold, martensitic state, may havea nearly closed, annular shape and, in response to heating, may enterinto the high-temperature austenite phase, the shape memory alloy beingshortened, so that the semifinished product opens; and, at thetransition to the low-temperature martensite phase, expands under theaction of the restoring force and returns to the nearly closed, annularshape, so that the semifinished product close. In the cold, martensiticstate, the alloy may have a smaller radius of curvature than in thewarm, austenitic state.

[0014] The present invention also provides method for manufacturing asemifinished product from a shape memory alloy having a two-way effect,wherein, in a deformation step carried out in the low-temperaturemartensite phase, besides the active martensitic/austenitic phase, alinear, superelastic phase is produced in the shape memory alloy,thereby introducing a restoring force to the alloy, so that, under theaction of this restoring force, the deformation cycle of the shapememory alloy is passed through several times during theaustenite/martensite phase transition.

[0015] As the result of deformation, stress distributions may beintroduced to the shape memory alloy, so that tensile and compressiveforces are produced, which lead to a curvature of the semifinishedproduct.

[0016] A bar-, band- or wire-shaped shape memory alloy may be drawn inthe cold martensitic state over a mandrel. After being drawn over themandrel, the shape memory alloy may be cut up into individual, curvedsections, without the stress distributions introduced to the shapememory alloy being thereby influenced; and the curved sections may besecured to a substrate.

[0017] During a process of weaving into fabric structures, a wire-shapedshape memory alloy may be drawn over lancets.

[0018] With the present invention, in the cold, martensitic state,besides the martensitic phase, the shape memory alloy exhibits adeformation-dependent linear elastic phase or linear superelastic phase,which results in a restoring force being produced in the shape memoryalloy itself, so that, at a high cycle number, a two-way effect isensured in the shape memory alloy because of the restoring force. Thelinear, superelastic phase is introduced by a single deformation step,which is implemented in the cold martensitic state.

[0019] The effect of the shape-memory-alloy deformation is that thelinear, superelastic phase is produced at the outer cross-sectional sideof the semifinished product made of the shape memory alloy, and, in thecold state, that the active martensitic phase resides in themid-cross-sectional area of the semifinished product. In response toheating, the martensitic phase enters into the austenitic phase, underdeformation of the shape memory alloy. In response to renewed coolingand transition into the martensitic phase, the shape memory alloyreturns to its previous shape under the action of the restoring forceproduced by the linear, superelastic phase.

[0020] As a result of the deformation, stress distributions arecontained in the shape memory alloy, so that tensile and compressiveforces are produced, which lead to a curvature of the semifinishedproduct made of the shape memory alloy. The tensile forces run on theouter curvature side and the compressive forces on the inner curvatureside of the semifinished product.

[0021] The shape memory alloy used is an alloy which, in principle, isable to exhibit a two-way effect. Ni—Ti alloys are used, for example.

[0022] Due to the linear, superelastic phase, which effects a restoringforce in the shape memory alloy, the external force required for thetwo-way effect, otherwise known as extrinsic two-way effect, is alreadyintegrated in the shape memory alloy, so that the force driving thetwo-way effect does not need to be externally supplied, nor is advancetraining of the shape memory alloy needed.

[0023] For this purpose, a bar-, band- or wire-shaped shape memory alloyis drawn in the cold martensitic state, in the longitudinal direction,over a mandrel under the action of force. This effects a deformation ofthe shape memory alloy and, thus, induces stress distributions, so thatthe linear, superelastic phase develops in the alloy. Following theprocessing step, the shape memory alloy assumes a curved or spiralshape. The shape memory alloy can subsequently be cut up intoindividual, curved sections and suitably secured to a substrate. In thismanner, one obtains curved alloy sections, which, in the cold,martensitic state, for example, form a nearly closed, annular mechanicalsticking [hook-like] element. The induced stress distribution and theresultant restoring force made available in the alloy are not influencedwhen the wire is cut up. If, under the action of heat, the shape memoryalloy enters into the austenitic phase, the alloy remembers its originalshape and, under shortening action, changes back to its original shape.The mechanical sticking element opens. When subsequently cooled, theshape memory alloy expands again under the action of the restoringforce. The mechanical sticking element closes. If it is then heatedagain, the connecting element opens. The cycle is run through again.

[0024] In accordance with another specific embodiment, a wire-shapedshape memory alloy, when woven into materials or fabric, is run in sucha way over lancets, that the one-time grazing over the lancets producesthe linear, superelastic phase in the shape memory alloy, so that thewoven-in alloy wire automatically passes repeatedly through theabove-described opening/closing operation during the cyclicalaustenite/martensite phase transition.

[0025] The advantage of the present invention lies in that a stabletwo-way effect is produced in simple fashion in the shape memory alloy,so that the semifinished product made of this shape memory alloy canpass repeatedly with a high effect stability through a deformationcycle. There is no need for a protracted training process for the shapememory alloy or for the action of external forces. Merely one processstep is necessary, which is implemented in the cold, martensitic state.

[0026] In addition, the present invention is distinguished bysubstantial variability, since the semifinished products are used invarious arrangements, such as in mechanically interlocking or fasteningelements. In addition, the method can be employed to manufacturesemifinished products of this kind in diverse ways, for example toproduce mechanically interlocking elements and loops, or it can be usedfor automatic weaving into fabric structures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be described in the following on thebasis of the figures, in which:

[0028]FIG. 1 shows, schematically, the representation of the method offunctioning of the two-way effect in a shape-memory alloy;

[0029]FIG. 2 shows, schematically, the representation of the method offunctioning of a shape memory alloy, which, in addition to the activemartensitic/austenitic phase, includes a linear, superelastic phase;

[0030]FIG. 3 shows the stress-strain profile of a shape memory alloy inthe martensitic state;

[0031]FIG. 4 shows the stress-strain profile of a linear super elasticmaterial of an Ni—Ti alloy;

[0032]FIG. 5 shows the schematic representation of the arrangement forintroducing selective deformations into the shape memory alloy;

[0033]FIGS. 6a, 6 b shows the schematic representation of thesemifinished product made of a shape memory alloy having a two-wayeffect in the cold and warm states, respectively; and

[0034]FIG. 7 shows the example of the deformation of an annular SMAelement made of an Ni—Ti wire having a 0.203 micrometer diameter.

DETAILED DESCRIPTION

[0035] First, the principle of the two-way effect is explained withreference to FIG. 1. In FIG. 1, reference numeral 1 denotes a bar-,band-, or wire-shaped shape memory alloy, in the following alsodescribed as SMA element. In the cold, martensitic state, SMA element 1is undeformed and, in initial state 1 a, exhibits a linear form. In thecold, martensitic state, SMA element 1 is deformed under the action of aforce, beyond the martensite plateau of the stress-strain profileillustrated in FIG. 3, in order to introduce plastic deformations by wayof dislocations into the alloy. Following the deformation, SMA element 1assumes annular shape 1 b. If one heats the alloy, a phase transitioninto the austenite follows, and only a portion of the reversibledeformation component returns to its previous form, because of theintroduced dislocations. Annular SMA element 1 does not pass completelyover into its initial state 1 a, but rather is shortened only to acertain extent and, therefore, opens. In this position 1 c, the radiusof curvature of SMA element 1 is greater than in closed state 1 b. Inresponse to cooling to the low-temperature martensite phase, the plasticstress fields existing around the dislocations produce martensitevariants, which transform the alloy into the desired low-temperatureshape. SMA element 1 again assumes shape 1 b. Due to the irreversiblecomponent, there is, therefore, a transformation from the cold, closed,annular state 1 b into open shape 1 c and back again into closed state 1b. The cycle can only be run through repeatedly if the shape memoryalloy had been previously trained; i.e., if the shape memory alloy hadrun through the deformation several times beforehand, so that, inresponse to cooling or heating, the shape memory alloy remembers theparticular shape; or an additional force acts externally upon the shapememory alloy.

[0036]FIG. 2 shows schematically the method of functioning of a shapememory alloy, which, in addition to the active martensitic/austeniticphase explained in conjunction with FIG. 1, includes a linear,superelastic phase. SMA element 1, which exhibits a linear initial state1 a, is deformed in the cold, martensitic state. As a result of thisdeformation, analogously to the case described in FIG. 1, plasticdeformations are produced in the alloy. In this deformation step,however, a linear, superelastic phase is produced at the same time. Thestress-strain profile of a linear super elastic material of this kind isshown in FIG. 4 for an Ni—Ti alloy. Tensile and compressive stresses areproduced in the longitudinal direction of the SMA element, so that, as aresult, a restoring force is produced within the shape memory alloyitself. The restoring force is indicated schematically in FIG. 2 by adotted line 2. Following the deformation, SMA element 1 assumes annularshape 1 b in the cold martensitic state. When making the transition tothe high-temperature austenite phase, the alloy remembers its originalshape, and annular SMA element 1 opens due to contraction of the alloy.In the process, the radius of curvature of annular SMA element 1increases. Due to the irreversible component, SMA element 1 does notpass over into its initial linear position 1 a, but rather into openposition 1 c. In response to subsequent cooling to the low-temperaturemartensite phase, the alloy expands under the action of the restoringforce contained in the alloy. Annular SMA element 1 closes and passesover into position 1 b. This closing movement is executed in oppositionto the compressive force running on the inner curvature side of SMAelement 1. At the same time, the action of the restoring force in themartensitic state effects an expansion of the alloy, so that the cyclecan be executed once more when the transition from martensite intoaustenite is made. In response to the phase transition into theaustenite, the alloy remembers its original shape and is shortened.Annular SMA element 1 opens in opposition to tensile forces running onthe outer side of the radius of curvature of SMA element 1. In contrastto the customary two-way effects discussed in FIG. 1, a simplificationis achieved by the combination of active martensitic/austenitic phasedescribed in FIG. 2 and the linear superelastic phase, which representsa gradient material. Due to the linear, superelastic phase introducedinto the shape memory alloy, and the restoring force produced by it, theforce required to expand the alloy during the austenite/martensite phasetransition is supplied by the alloy itself, so that no external force ortraining is necessary. The martensite/austenite phase transition can bereliably repeated for a large number of cycles.

[0037] As described in conjunction with FIG. 2, in addition to themartensitic phase present in the cold state of the shape memory alloy, alinear, superelastic phase is introduced into the alloy. This isachieved by one single deformation step, which simultaneously producesthe pseudo-plastic or plastic deformation of the martensitic phase.Alternatively, the deformation can also be carried out for theparticular phase in separate steps as well, which will not be discussedin detail here, however.

[0038] At this point, it will be explained in conjunction with FIG. 5,how the linear, superelastic phase is introduced to the shape memoryalloy. A bar-, band- or wire-shaped shape memory alloy 1 is drawn in thecold martensitic state, with the aid of a conveyor mechanism 3, over amandrel 4, and weighted by a load 4. In the process, SMA element 1 isconveyed with a curvature over mandrel 4. The loading is carried out inthe longitudinal direction of the bar-, band- or wire-shaped SMA element1, whose longitudinal extension is substantially greater than itscross-sectional dimension. The drawing over mandrel 4 can beaccomplished manually using muscular force, or in some other suitablemanner. The set-up shown in FIG. 5 is merely one example. One canconceive of a multiplicity of other ways for attaining the properelongation or deformation of SMA element 1.

[0039] By drawing SMA element 1 once in its longitudinal direction overmandrel 4, shape memory alloy 1 is deformed such that a linear,superelastic phase is produced in the shape memory alloy. Thestress-strain profile of a linear, superelastic phase of this kind isshown in FIG. 4 for an Ni—Ti alloy. Corresponding tensile andcompressive stress distributions are produced within the shape memoryalloy. This is elucidated on the basis of FIGS. 6a and 6 b.

[0040]FIGS. 6a and 6 b show a semifinished tool made of a shape memoryalloy exhibiting the two-way effect described in the context of FIG. 2.The semifinished product is composed of a curved section of aselectively deformed bar-, band-, or wire-shaped shape memory alloy.Following the deformation step, curved regions are cut out, resulting,in the cold state, in the nearly closed, annular shape in FIG. 6a. Thesemifinished products can be integrated in different ways in alreadyexisting fabric, to form, for example, a connecting or mechanicalinterlocking element. A plurality of such loops or hooks can also beplaced separately, side-by-side, on a suitable substrate.

[0041]FIG. 6a shows the semifinished product in a nearly closed, annularshape in the cold, martensitic state. Due to the introduced deformation,tensile forces are produced on the outer curvature side of thesemifinished product, and compressive forces on the inner curvatureside, as shown in FIGS. 6a and 6 b, respectively, by dotted lines. Thecurved SMA semifinished product illustrated in FIGS. 6a and 6 b thusexhibits, on the outer peripheral sides, a linear, superelastic phaseand, in the middle region, an active martensitic/austenitic phase. Theactive martensitic/austenitic phase means that this is the phase of theshape memory alloy which, in response to the temperature-dependent phasetransition, passes over from the martensitic into the austenitic stateand vice versa. It is, therefore, this middle region which carries outthe deformation described in conjunction with FIG. 1. The outer region,namely the linear, superelastic phase, provides, in this context, therestoring force needed for the deformation from the austenitic to themartensitic state. Thus, in response to heating, the martensitic phasepasses over to the high-temperature austenite phase, and shortening ofthe alloy causes the annular SMA semifinished product to open. Thesubsequent cooling produces an expansion under the action of therestoring force. The annular SMA semifinished product closes in responseto the radius of curvature becoming smaller. The opening/closingmechanism can be run through repeatedly with a high effect stability.

[0042] Besides the drawing of the bar-, band- or wire-shaped shapememory alloy over a mandrel, and subsequent cutting and positioning ofthe curved SMA sections, the deformation process can also be carried outautomatically, for example, by weaving the sections into selectedstructures. For this, an SMA wire to be woven in can be run overlancets, so that, on the one hand, by grazing the wire over the lancets,the linear, superelastic phase is introduced to the material and, at thesame time, the alloy is deformed in the martensitic phase beyond themartensite plateau. Thus, the then woven-in shape memory alloy exhibitsthe two-way effect discussed in connection with FIG. 2, so that, inresponse to temperature changes, the shape memory alloy passes over intocorresponding deformation states.

[0043] Semifinished products of this kind and the corresponding methodcan be used, for example, in the manufacturing of releasable VELCRO-typefasteners. In this connection, individual, annular SMA elements depictedin FIGS. 6a and 6 b can be worked manually into existing fabriccomponents of VELCRO-type fasteners, enabling the fastener to bedetached or closed under the influence of a temperature change. Theworking-in can also be carried out automatically, however, when weavingthe fabric structures. In this case, the semifinished product is theshape-memory-alloy wire that is stiffened by the lancets.

EXAMPLE

[0044] A wire made of an Ni—Ti alloy (54.76 wt % nickel, 45.23 wt %titanium, carbon concentration and oxygen concentration less than 500ppm) having a diameter of 0.203 μm, was drawn one time over a mandrelhaving a 1 mm diameter. As a result, the wire took on a spiral shape.The wire was subsequently cut in such a way that closed wire loops orhooks were obtained. Annular hooks were subsequently secured to asubstrate. Two nearly closed hooks of this kind are shown in FIG. 7. Ifthe Ni—Ti wire is heated, the alloy remembers its original shape and,under deformation, passes over to the austenitic phase. In this case,the wire is shortened in response to this phase transition, so that theradius of curvature is enlarged, and an opening is formed between thepreviously nearly closed hooks. The opening angle in the example shownin FIG. 7 amounts to 30.8° and 26°. In this instance, the wire ends arespaced apart by 2.58 mm and 2.19 mm, respectively. In response torenewed cooling, the wire passes over again into the low-temperaturemartensite phase, a closed position, including a smaller radius ofcurvature, resulting because of the linear expansion under the action ofthe restoring force contained in the alloy.

What is claimed is:
 1. A semifinished product comprising: a shape memoryalloy, the shape memory alloy including an active martensitic/austeniticphase and a linear, superelastic phase forming a restoring force in theshape memory alloy, the shape memory alloy capable of running through adeformation cycle several times during an austenite/martensite phasetransition under action of the restoring force.
 2. The semifinishedproduct as recited in claim 1, wherein the alloy has an outercross-sectional side and a mid-cross-sectional area, the linear,superelastic phase being situated at the outer cross-sectional side andthe active martensitic/austenitic phase being situated in themid-cross-sectional area; in response to heating, the martensitic phaseentering into the austenitic phase, under deformation of the shapememory alloy, and, in response to cooling, returning to the martensiticphase, the shape memory alloy returning to a shape before deformation,through the action of the restoring force.
 3. The semifinished productas recited in claim 1, wherein the shape memory alloy has stressdistributions, so that tensile and compressive forces are produced whichlead to a curvature of the semifinished product.
 4. The semifinishedproduct as recited in claim 3, wherein the tensile forces run on anouter curvature side and the compressive forces on an inner curvatureside of the semifinished product.
 5. The semifinished product as recitedin claim 1, wherein the shape memory alloy is an alloy capable ofexhibiting a two-way effect.
 6. The semifinished product as recited inclaim 1, wherein the shape memory alloy is composed of 55 wt % nickeland of 45 wt % titanium.
 7. The semifinished product as recited in claim1, wherein, in a cold, martensitic state, the shape memory alloy has anearly closed, annular shape and, in response to heating, enters into ahigh-temperature austenite phase, the shape memory alloy beingshortened, so that the semifinished product opens; and, at a transitionto the low-temperature martensite phase, expands under the action of therestoring force and returns to the nearly closed, annular shape.
 8. Thesemifinished product as recited in claim 7, wherein, in the cold,martensitic state, the product has a smaller radius of curvature than inthe warm, austenitic state.
 9. A method for manufacturing a semifinishedproduct from a shape memory alloy having a two-way effect comprising thesteps of: carrying in out a deformation step in the low-temperaturemartensite phase of an active martensitic/austenitic phase, andproducing a linear, superelastic phase in the shape memory alloy so asto introduce a restoring force to the alloy, so that, under the actionof the restoring force, a deformation cycle of the shape memory alloy ispassed through several times during an austenite/martensite phasetransition.
 10. The method as recited in claim 9, wherein the shapememory alloy is deformed such that the linear, superelastic phase isproduced at an outer cross-sectional side of the semifinished product,and, in the cold state, the martensitic phase is in amid-cross-sectional area of the semifinished product; in response toheating, the martensitic phase entering into an austenitic phase, underdeformation of the shape memory alloy, and, in response to cooling ofthe martensitic phase, the shape memory alloy returning to the shapebefore deformation under the action of the restoring force.
 11. Themethod as recited in claim 9, wherein, as the result of deformation,stress distributions are introduced to the shape memory alloy, so thattensile and compressive forces are produced, which lead to a curvatureof the semifinished product.
 12. The method as recited in claim 9,wherein the shape memory alloy is in a bar-, band- or wire shape andfurther comprising drawing the shape memory alloy in a cold martensiticstate over a mandrel.
 13. The method as recited in claim 12, furthercomprising cutting the shape memory alloy into individual, curvedsections, without the stress distributions introduced to the shapememory alloy being thereby influenced; and securing the curved sectionsto a substrate.
 14. The method as recited in claim 9, wherein the alloyis in a wire shape and further comprising weaving the alloy into fabricstructures, the wire-shaped shape memory alloy being drawn over lancets.15. A curved semifinished product made of a shape memory alloycomprising: an outer surface including an active martensitic/austeniticphase; and a section interior to the outer surface including a linear,superelastic phase forming a restoring force in the shape memory alloy,the curved product having an opening capable of widening and narrowingunder action of the restoring force.